This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Objective: To investigate whether there is any secular trend in body weight increase and early timing of puberty in rhesus monkeys in our colony. During the course of the 30-year studies, the age of menarche in experimental animals had become gradually younger, yet the body weight at menarche was the same. Thus, we have hypothesized that there is a secular trend in body weight increase and early onset of puberty in our colony monkeys. Extensive analysis of the colony records indicates that the body weight growth curve gradually left-shifted during the past 30 years in both females and males. Moreover, the age of menarche in colony females also became significantly younger during this period. Analysis of feeding programs during this period further suggested that monkeys in our current colony were fed a higher calorie diet than those 30 years ago. This secular trend towards obesity and menarche at younger ages in the WNPRC colony monkeys is strikingly similar to the trend in human society. The mechanism of body weight impact on puberty remains to be investigated. This research used WNPRC Animal Services and Information Services.